Ratiometric fluorescent detection of Cu2+ based on dual‐emission ZIF‐8@rhodamine‐B nanocomposites

Zeolitic imidazolate framework‐8 (ZIF‐8) loading rhodamine‐B (ZIF‐8@rhodamine‐B) nanocomposites was proposed and used as ratiometric fluorescent sensor to detect copper(II) ion (Cu²⁺). Scanning electron microscopy, Fourier transform infrared spectroscopy, X‐ray powder diffraction, nitrogen adsorption/desorption isotherms and fluorescence emission spectroscopy were employed to characterize the ZIF‐8@rhodamine‐B nanocomposites. The results showed the rhodamine‐B was successfully assembled on ZIF‐8 based on the π‐π interaction and the hydrogen bond between the nitrogen atom of ZIF‐8 and –COOH of rhodamine‐B. The as‐obtained ZIF‐8@rhodamine‐B nanocomposites were octahedron with size about 150–200 nm, had good water dispersion, and exhibited the characteristic fluorescence emission of ZIF‐8 at 335 nm and rhodamine‐B at 575 nm. The Cu²⁺ could quench fluorescence of ZIF‐8 rather than rhodamine‐B. The ZIF‐8 not only acted as the template to assemble rhodamine‐B, but also was employed as the signal fluorescence together with the fluorescence of rhodamine‐B as the reference to construct a novel ratiometric fluorescent sensor to detect Cu²⁺. The resulted ZIF‐8@rhodamine‐B nanocomposite fluorescence probe showed good linear range (68.4 nM to 125 μM) with a low detection limit (22.8 nM) for Cu²⁺ combined with good sensitivity and selectivity. The work also provides a better way to design ratiometric fluorescent sensors from ZIF‐8 and other fluorescent molecules.     

Reviving near infra‐red emission of Ag2S nanoparticles using interfacial defects in the Ag2S@CdS core–shell structure

Ag₂S@CdS core–shell particles were synthesized with different Cd source content as a measure of shell thickness using a pulsed microwave irradiation method. The particles were verified structurally using X‐ray diffraction, energy dispersive X‐ray analysis and transmission electron microscopy. Optical spectroscopy revealed that core–shells show an absorption peak at 750 nm and an emission peak located around 800 nm after 6 min of microwave irradiation. With continued microwave treatment, the NIR luminescence first vanished but it was revived after 12 min of irradiation, which was 100 nm red shifted. This new type of NIR emission in Ag₂S with sizes greater than 5 nm is due to the proximity of a highly deficient CdS shell with strong red emission that was stable for more than 6 months in water. A mechanism has been suggested for this type of emission.     

Enhanced photoluminescence properties of electrospun Dy3+‐doped ZnO nanofibres for white lighting devices

Dy³⁺‐doped ZnO nanofibres with diameters from 200 to 500 nm were made using an electrospinning technique. The as‐fabricated amorphous nanofibres resulted in good crystalline continuous nanofibres through calcination. Dy³⁺‐doped ZnO nanofibres were characterized using scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDX), X‐ray diffraction (XRD), ultraviolet–visible (UV–vis) light spectroscopy, Fourier transform infrared spectroscopy (FTIR), and photoluminescence (PL). XRD showed the well defined peaks of ZnO. UV–vis spectra showed a good absorption band at 360 nm. FTIR spectra showed a Zn–O stretching vibration confirming the presence of ZnO. Photoluminescence spectra of Dy³⁺‐doped ZnO nanofibres showed an emission peak in the visible region that was free from any ZnO defect emission. Emissions at 480 nm and 575 nm in the Dy³⁺‐doped ZnO nanofibres were the characteristic peaks of dopant Dy³⁺ and implied efficient energy transfer from host to dopant. Luminescence intensity was found to be increased with increasing doping concentration and reduction in nanofibre diameter. Colour coordinates were calculated from photometric characterizations, which resembled the properties for warm white lighting devices.     

Silver‐doped graphite carbon nitride nanosheets as fluorescent probe for the detection of curcumin

Green fluorescent silver (Ag)‐doped graphite carbon nitride (Ag‐g‐C₃N₄) nanosheets have been fabricated by an ultrasonic exfoliating method. The fluorescence of the Ag‐g‐C₃N₄ nanosheets is quenched by curcumin. The fluorescence intensity decreases with the increase in the concentration of curcumin, indicating that the Ag‐g‐C₃N₄ nanosheets can function as a non‐toxic and facile fluorescence probe to detect curcumin. The fluorescence intensity of Ag‐g‐C₃N₄ nanosheets shows a linear relationship to curcumin in the concentration range 0.01–2.00 μM with a low detection limit of 38 nM. The fluorescence quenching process between curcumin and Ag‐g‐C₃N₄ nanosheets mainly is based on static quenching. The fluorescent probe has been successfully applied to analyse curcumin in human urine and serum samples with satisfactory results.     

High quantum yield and well‐dispersed quantum dots luminescent composite through sodium carboxymethyl starch

It is a challenging task to prepare well‐dispersed and highly luminescent quantum dots (QDs) powder and a new strategy is reported in this article. Sodium carboxymethyl starch (CMS‐Na) was employed in this work to prepare the QDs–starch composite. Ultraviolet (UV) light shows that the blank starches had no fluorescence, while the QDs‐starches were highly luminescent. Scanning electron microscopy (SEM) observation shows that the QDs–starch composite has the typical particle morphology with the diameter around 200 nm. Energy dispersive X‐ray spectroscopy (EDX) results show that there are intensive tellurium (Te) and cadmium (Cd) element signals. Combined fluorescent lifetime and steady‐state spectrometer show that the QDs–starch quantum yields (QYs) increase when the QDs loading increases from 1 × 10^?6 mol/g to 2 × 10^?6 mol/g, but when the loadings further increase, the QYs decrease slightly. For the red colour (λ_em = 660 nm) QDs, the QYs can reach to as high as 28.2%, and for the other colour QDs they can also have the QYs above 22%. Time‐resolved photobleaching experiments show that the fluorescent QDs–starch composite has a half‐decay time of 40.23 s. These results indicate that the CMS‐Na is a promising QDs dispersant to obtain high QY QD composites.     

Photophysical and structural aspects of perylene‐doped 2‐naphthol luminophors: Green emission by exciplex formation

Several perylene (Pery)‐doped 2‐naphthol (2‐NP) (Pery/2‐NP) luminophors were prepared using conventional solid‐state reaction techniques. Energy transfer in the excited state was examined using fluorescence spectroscopy and cyclic voltammetry. Fluorescence studies revealed exciplex formation by Pery in the form of structureless and broad spectra at higher concentrations with monomer quenching of 2‐NP; a broad green emission was observed in the range 500–650 nm, peaking at 575 nm. Structural properties and thermal stability were analyzed using X‐ray diffraction, scanning electron microscopy and TGA‐differential scanning calorimetry. Highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels were observed in the range 5.56–5.61 eV and 2.79–2.81 eV, respectively with a 2.77–2.82 eV band gap. The present study reveals these to be probable candidates for hole‐transporting materials suitable in optoelectronics.     

Preparation and application of solvent‐modulated self‐doped N–S multicolour fluorescence carbon quantum dots

In this paper, two types of carbon quantum dot (CQDs) were prepared using biocompatible l ‐methionine as the carbon source and urea as the nitrogen source and a one‐step hydrothermal treatment. By changing the reaction solvents (deionized (DI) water and dimethylformamide (DMF)), the maximum emission of the resulting CQDs shifted from blue to red light. Specifically, the emission wavelength of the CQDs moved from 433 nm to 625 nm following embedding of a new functional group (–CONH–) on the surface of the CQDs. Photoluminescence quantum yields of the CQDs with blue and red emission reached 64% and 61%, respectively. The R‐CQDs were used to detect metal ions and a linear relationship was demonstrated between ln(F/F₀) and Fe³⁺ concentration in the range 0–0.5 mmol/L with a detection limit of 0.067 μM. Therefore these R‐CQDs have great potential as fluorescent probes for Fe³⁺ detection. We expect that the excellent water‐soluble, biocompatible and optical properties of the CQDs developed in this work mean that they will be widely used to detect biological cells.     

Novel optical properties of Ca12Al10.6Si3.4O32Cl5.4:Ce3+,Li+ phosphor for solid‐state lighting

This article reports a novel blue emission in a series of Ca₁₂Al_10.6Si_3.4O₃₂Cl_5.4:Ce³⁺ phosphor under excitation in the near‐UV wavelength range. This phosphor was prepared using the combustion method. Here, the Ce³⁺ emission band is observed over a broad range of 380–550 nm, under 365 nm excitation, and is due to 5d–4f transition. The effect of a Li⁺ charge compensator on the emission properties of the phosphor was also investigated for the first time. X‐Ray diffraction confirmed the phase purity of the synthesized phosphor. The surface morphology and elemental composition of the phosphor were studied using scanning electron microscopy and energy‐dispersive X‐ray spectroscopy. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis,structure and density functional theory calculations of a novel photoluminescent trisarylborane–bismuth(III) complex

A novel trisarylborane–Bi(III) complex, tris(4‐(dimesitylboryl)phenyl)bismuthine [Bi(PhBMes₂)₃], in which (Ph = phenyl, and Mes = mesityl), was synthesized via the reaction of bismuth (III) chloride (BiCl₃) with three equivalents of lithiated (4‐bromophenyl)‐ dimesitylborane [BrPhBMes₂]. The new trisarylbismuthine was characterized by elemental analysis, ultraviolet–visible (UV–vis) spectroscopy, and NMR (¹H and ¹³C) spectroscopy. The molecular structure of Bi(PhBMes₂)₃ in the solid state was determined using single‐crystal X‐ray diffraction analysis, which showed short intermolecular C–H···H–C contact. The complex is a fluorescent emitter (λ_max = 395 nm) at room temperature and a phosphorescent emitter (λ_max = 423 nm) at 77 K, which displayed a long lifetime of 495 ms. The UV–vis transitions were investigated using density function theory (DFT) and time‐dependent (TD)‐DFT calculations. Natural bond orbital analysis showed that the bismuth (III) center was mainly Lewis acidic in nature.     

UV light‐tunable fluorescent inks and polymer hydrogel films based on carbon nanodots and lanthanide for enhancing anti‐counterfeiting

Novel water‐soluble green fluorescent carbon nanodots (CNs) using methacrylic acid and m‐phenylenediamine as precursors were first synthesized using a one‐pot hydrothermal method. Red fluorescent lanthanide complexes were prepared using lanthanide ion Eu³⁺ and pyridine‐2,6‐dicarboxylic acid. The optical properties of CNs were characterized using ultraviolet visible (UV) spectra and fluorescence spectra, microscopic morphology was characterized using transmission electron microscopy (TEM) and dynamic light scattering (DLS), and the elemental composition was characterized using Fourier transform‐infrared spectroscopy (FT‐IR) and X‐ray photoelectron spectra (XPS). The fluorescence spectra of the lanthanide complexes were also measured. A simple strategy was developed to prepare UV light‐tunable fluorescent inks and polymer hydrogels films based on CNs and lanthanide complexes. The fluorescent inks and polymer hydrogels films could be repeatedly switched between green and red fluorescence. The change of color depended on luminescence of the CNs and the lanthanide complexes under 254 and 365 nm UV light, respectively. The UV light‐tunable fluorescent inks and polymer hydrogels films could enhance its anti‐counterfeiting function for data and information.     

Structural and photoluminescence study of Mn2+‐activated CaYAl3O7 blue phosphors

The structural and photoluminescence properties of CaYAl₃O₇ phosphor material doped with varying concentration of Mn²⁺ have been studied. The phosphor material was synthesized by the combustion method at 500 °C and was characterized using X‐ray diffraction, Fourier transform infrared spectroscopy and photoluminescence spectroscopy (PL). X‐ray diffraction showed that the crystallites have average sizes in the range of ~58–70 nm. Corresponding Fourier transform infrared spectroscopy investigations confirm the phase formation and the presence of aluminate group (Al‐O bands) in CaYAl₃O₇:Mn²⁺ phosphor. Under the excitation at 356 nm wavelength, the PL spectra show the occurrence of two emission peaks obtained in the blue region at 389 nm and 412 nm, which is attributed to the 4 T1(G) → 6A1 transition of Mn²⁺ ion. Upon increasing Mn²⁺ concentration, the relative PL intensity shows an initial decrement followed by an increase displaying the effect of concentration quenching. Overall the results suggest the possibility of using this material in white lighting devices and plasma display panels. Copyright © 2013 John Wiley & Sons, Ltd.     

An efficient orange–red‐emitting LiNa3P2O7:Sm3+ pyrophosphate: Structural and optical analysis for solid‐state lighting

A trivalent rare‐earth ion (Sm³⁺)‐doped LiNa₃P₂O₇ (LNPO) phosphor was synthesized using a conventional high‐temperature solid‐state reaction route. A predominant orthorhombic phase of LNPO was observed in all X‐ray diffraction patterns. The surface states of the LNPO:Sm phosphor were confirmed by X‐ray photoelectron spectroscopy. Under 401 nm excitation, the Sm‐doped LNPO phosphors showed sharp emission peaks at 563, 600 and 647 nm that are related to the f–f transition of Sm³⁺ ions. The optimum concentration of Sm³⁺ (9 mol%) produced Commission Internationale de l'Eclairage chromaticity coordinates, color rendering index and correlated color temperature of (0.564, 0.434), 42 and 1843 K, respectively.     

Preparation of carbon dot‐based ratiometric fluorescent probes for cellular imaging from Curcuma longa

This work derived biocompatible and stable probes based on fluorescent nanoparticles (FNPs) from a natural source, Curcuma longa. The multi‐color fluorescence emissions from carbonized Curcuma longa (C‐FNPs) obtained through defined dehydration conditions are soluble in water and have a small particle size (~17 nm). The surface passivation with polyethylene glycol (PEG) capped with amine groups in FNPs (P‐FNPs) generated a probe with a higher quantum yield and longer fluorescence lifetime than obtained with C‐FNPs. The X‐ray photoelectron spectroscopy and X‐ray diffraction spectra confirmed the associated chemical moieties of C‐FNPs and P‐FNPs. Furthermore, the prepared material showed non‐toxic effects with almost 100% cell viability, even at high concentrations. In conclusion, fluorescence sensors from natural sources may be useful for numerous biomedical research applications.     

Luminescence investigation of a cerium‐doped yttrium vanadate phosphor

Cerium (Ce³⁺)‐doped (1, 3, and 7 mol%) yttrium vanadate phosphors were prepared using a co‐precipitation technique. The structural and optical properties of the synthesized samples were studied using X‐ray diffraction (XRD), Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), high‐resolution transmission electron microscopy (HR‐TEM), optical absorption, and photoluminescence (PL) spectroscopy techniques. The tetragonal structure and the formation of the nanosized crystallites in the YVO₄:Ce phosphor were confirmed using XRD analysis. HR‐TEM morphology showed rod‐like nanoparticles of different sizes. Optical absorption spectra demonstrated strong absorption bands at 268 and 276 nm. PL spectra showed strong peaks at 546, 574, and 691 nm following excitation at 300 nm. The calculated CIE chromaticity coordinates demonstrated that YVO₄:Ce could be used as a novel phosphor for the development of light‐emitting diode lamps.     

Hydrothermal synthesis for high‐quality glutathione‐capped CdxZn1 – xSe and CdxZn1 – xSe/ZnS alloyed quantum dots and its application in Hg(II) sensing

High‐quality Cd_xZn_{1 – x}Se and Cd_xZn_{1 – x}Se/ZnS core/shell quantum dots (QDs) emitting in the violet–green spectral range have been successfully prepared using hydrothermal methods. The obtained aqueous Cd_xZn_{1 – x}Se and Cd_xZn_{1 – x}Se/ZnS QDs exhibit a tunable photoluminescence (PL) emission (from 433.5 nm to 501.2 nm) and a favorable narrow photoluminescence bandwidth [full width at half maximum (FWHM): 30–42 nm]. After coating with a ZnS shell, the quantum yield increases from 40.2% to 48.1%. These Cd_xZn_{1 – x}Se and Cd_xZn_{1 – x}Se/ZnS QDs were characterized by transmission electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy and Fourier transform infrared (FTIR) spectroscopy. To further understand the alloying mechanism, the growth kinetics of Cd_xZn_{1 – x}Se were investigated through measuring the fluorescence spectra and X‐ray diffraction spectra at different growth intervals. The results demonstrate that the inverted ZnSe/CdSe core/shell structure is formed initially after the injection of Cd²⁺. With further heating, the core/shell structured ZnSe/CdSe is transformed into alloyed Cd_xZn_{1 – x}Se QDs with the diffusion of Cd²⁺ into ZnSe matrices. With increasing the reaction temperature from 100 °C to 180 °C, the duration time of the alloying process decreases from 210 min to 20 min. In addition, the cytotoxicity of Cd_xZn_{1 – x}Se and Cd_xZn_{1 – x}Se/ZnS QDs were investigated. The results indicate that the as‐prepared Cd_xZn_{1 – x}Se/ZnS QDs have low cytotoxicity, which makes them a promising probe for cell imaging. Finally, the as‐prepared Cd_xZn_{1 – x}Se/ZnS QDs were utilized to ultrasensitively and selectively detect Hg²⁺ ions with a low detection limit (1.8 nM).     

Green synthesis and physiochemical characterization of nickel oxide nanoparticles: Interaction studies with Calf thymus DNA

One of the most promising applications of nanomaterials is that of nanobiosensors, using biomolecules such as nucleic acids as receptors. This study aimed to synthesize nickel oxide nanoparticles (NiO NPs) by an environmentally friendly green synthesis, using the extract of the herb Coriandrum sativum (coriander). The synthesized NPs were characterized using UV–Visible spectroscopy, Fourier transform infrared spectroscopy, X‐ray diffraction, X‐ray photon spectroscopy, field emission scanning electron microscopy coupled with energy dispersive spectroscopy, dynamic light scattering, zeta potential and transmission electron microscopy. All results confirmed the synthesis of pure, spherical, positively charged NiO NPs of around 95 nm in diameter with prominent hydroxyl groups attached to the surface. Furthermore, interaction studies of synthesized NiO NPs with calf thymus DNA (CT DNA) were performed using UV–Visible spectroscopy, UV–thermal melting, circular dichroism, and fluorescence spectroscopy. CT DNA served as a substitute for nucleic acid biosensors. All experimental studies indicated that the NiO NPs bound electrostatically with CT DNA. These studies may facilitate exploring the potential of NiO NP–nucleic acid conjugated materials to be used as nanobiosensors for various applications, especially in pharmacological, epidemiological, and environmental diagnostic applications, and in detection.     

Study of luminescence properties of dysprosium‐doped CaAl12O19 phosphor for white light‐emitting diodes

Dy³⁺‐doped CaAl₁₂O₁₉ phosphors were synthesized utilizing a combustion method. Crystal structure and morphological examinations were performed respectively using X‐ray diffraction (XRD) and scanning electron microscopy (SEM) techniques to identify the phase and morphology of the synthesized samples. Fourier transform infrared spectroscopy (FTIR) estimations were carried out using the KBr method. Photoluminescence properties (excitation and emission) were recorded at room temperature. CaAl₁₂O₁₉:Dy³⁺ phosphor showed two emission peaks respectively under a 350‐nm excitation wavelength, centered at 477 nm and 573 nm. Dipole–dipole interaction via nonradiative energy shifting has been considered as the major cause of concentration quenching when Dy³⁺ concentration was more than 3 mol%. The CIE chromaticity coordinates positioned at (0.3185, 0.3580) for the CaAl₁₂O₁₉:0.03Dy³⁺ phosphor had a correlated color temperature (CCT) of 6057 K, which is situated in the cool white area. Existing results point out that the CaAl₁₂O₁₉:0.03Dy³⁺ phosphor could be a favorable candidate for use in white light‐emitting diodes (WLEDs).     

Quasi‐spherical silver nanoparticles with high dispersity and uniform sizes: preparation,characterization and bioactivity in their interaction with bovine serum albumin

A stepwise seeded growth route for the preparation of silver nanoparticles (AgNPs) is reported. In the process, silver nitrate was used as a precursor, with sodium borohydride as a reducing agent and trisodium citrate as both a reductant and stabilizer. The AgNPs were characterized using several methods, including UV–vis spectroscopy, X‐ray diffraction and transmission electron microscopy. The prepared AgNPs were quasi‐spherical and crystalline, with an average diameter of 21 nm. Interactions between the AgNPs and bovine serum albumin (BSA) were investigated using UV–vis, fluorescence spectroscopy and synchronous fluorescence spectroscopy (SFS). It was proved that the quenching mechanism is a static process. The binding constants and number of binding sites were calculated. The thermodynamic parameters implied that the binding process was spontaneous and the main driving force of the interaction was electrostatic. The results of the SFS indicated that the conformational change of BSA was induced by AgNPs. Copyright © 2016 John Wiley & Sons, Ltd.     

Facile preparation of high fluorescent carbon quantum dots from orange waste peels for nonlinear optical applications

A facile and eco‐friendly hydrothermal method was used to prepare carbon quantum dots (CQDs) using orange waste peels. The synthesized CQDs were well dispersed and the average diameter was 2.9 ± 0.5 nm. Functional group identification of the CQDs was confirmed by Fourier transform infrared spectrum analysis. Fluorescence properties of the synthesized CQDs exhibited blue emission. The fluorescence quantum yield of the CQDs was around 11.37% at an excitation wavelength of 330 nm. The higher order nonlinear optical properties were examined using a Z‐scan technique and a continuous wave laser that was operated at a wavelength of 532 nm. Results demonstrated that the synthesis of CQDs can be considered as promising for optical switching devices, bio‐scanning, and bio‐imaging for optoelectronic applications.     

Silica‐modified luminescent LaPO4:Eu@LaPO4@SiO2 core/shell nanorods: Synthesis,structural and luminescent properties

Monoclinic‐type tetragonal LaPO₄:Eu (core) and LaPO₄:Eu@LaPO₄ (core/shell) nanorods (NRs) were successfully prepared using a urea‐based co‐precipitation process under ambient conditions. An amorphous silica layer was coated around the luminescent core/shell NRs via the sol–gel process to improve their solubility and colloidal stability in aqueous and non‐aqueous media. The prepared nano‐products were systematically characterized by X‐ray diffraction pattern, transmission electron microscopy, energy dispersive X‐ray analysis, and FTIR, UV/Vis, and photoluminescence spectroscopy to examine their phase purity, crystal phase, surface chemistry, solubility and luminescence characteristics. The length and diameter of the nano‐products were in the range 80–120 nm and 10–15 nm, respectively. High solubility of the silica‐modified core/shell/Si NRs was found for the aqueous medium. The luminescent core NRs exhibited characteristic excitation and emission transitions in the visible region that were greatly affected by surface growth of insulating LaPO₄ and silica layers due to the multiphonon relaxation rate. Our luminescence spectral results clearly show a distinct difference in intensities for core, core/shell, and core/shell/Si NRs. Highly luminescent NRs with good solubility could be useful candidates for a variety of photonic‐based biomedical applications.